package dptest;

public class t1137 {
 public static void main(String[] args) {
	 
	 int n = 25;
	 /*if(n == 0) {
		 return 0 ;
	 }else if(n == 1) {
		 return 1;
	 }else if(n == 2) {
		 return 1 ;
	 }*/
	int dp [] = new int[n+1];
	dp[0] = 0; dp[1] = 1; dp[2] = 1;
	for(int i = 3; i<=n;i++) {
		dp[i] = dp[i-3]+dp[i-2]+dp[i-1];
	}
	//return dp[n];
	System.out.println(dp[n]);
}
}
